Hypoxia is a deficiency of blood reaching tissues and organs of the body which is generally associated with a drop in the blood oxygen level. When hypoxia occurs, the individual becomes disoriented and confused. An extreme loss of oxygen over a sufficient period of time will cause the individual to become unconscious.
This is a severe problem with pilots. If a pilot becomes disoriented or unconscious for even a very brief period of time, a crash can occur. Hypoxia is a particularly significant problem with pilots because of the decrease in oxygen level at higher altitudes. If a pilot breathes ambient air, at a sufficiently high altitude, the loss of oxygen in the ambient air can cause hypoxia. A second cause of hypoxia call be breathing exhaust from the airplane engine. Although airplanes are certainly designed to prevent engine exhaust from entering the cockpit area, this can occur. The carbon monoxide contained in such gases will enter the blood stream and prevent oxygenation of the blood, and thus, a decrease in blood oxygen level.
In the past, there have been invasive methods used to monitor blood oxygen levels of astronauts. However, invasive methods are unsuitable for pilots. Any system for pilots must be noninvasive and very simple to operate.